Improving Exchanger Performance

Sometimes, the problem to be solved is simple – poor thermal performance.  Although heat exchanger designers always aim for high heat transfer coefficients this can sometimes be difficult to achieve with a conventional plain tube design.  In many cases this is due to the properties of the tubeside fluid such as high viscosity and/or low thermal conductivity. Occasionally, low heat transfer rates are a consequence of the arrangement of the exchanger such as when single pass tube bundles are required.

Whatever the reasons, poor tubeside performance can usually be avoided by considering the use of heat transfer enhancement technologies.  Engineered devices such as hiTRAN Matrix Elements invariably provide increased heat transfer coefficients relative to plain tubes.

Increasing Heat Transfer Rates with Enhancement

Graphical representation of plain tube heat transfer against hiTRAN enhanced performance range

hiTRAN Matrix Elements Performance Graph

hiTRAN Matrix Elements Performance Graph

When fluid flows through a plain tube the fluid nearest the wall is subjected to frictional drag, which has the effect of slowing down the fluid at the wall. This laminar boundary layer can significantly reduce the tubeside heat transfer coefficient and consequently, the performance of the heat exchanger.

Inserting correctly profiled hiTRAN Matrix Elements into the tube will disrupt the laminar boundary layer, creating additional fluid shear and mixing, thereby minimizing the effects of frictional drag. hiTRAN Wire Turbulators are particularly effective at enhancing heat transfer efficiency in tubes  operating at low Reynolds numbers (laminar to transitional flow.) Although the heat transfer increase is greatest in the laminar flow region (up to 16 times), significant benefits can be obtained in the transitional flow regime (up to 12 times) and turbulent flow regime (up to 3 times). Cal Gavin have installed hiTRAN Systems in heat exchangers operating with Reynolds numbers from 1 to over 100,000.

Whilst there is an increase in frictional resistance associated with hiTRAN Systems, the amount of enhancement is such that solutions can be found which offer increased heat transfer at equivalent or lower pressure drop than a plain tube.

Case study examples illustrating improved performance

Below are some brief descriptions of projects CALGAVIN have enhanced previously. For a more comprehensive range please see the case studies page.

HCGO/ tempered water cooler

(CS9) New heavy cycle gas oil cooler designed with 80% reduced surface area provides consistent performance without usual sticky deposit formation IMPERIAL OIL

Heating cracked bottoms and coal tar mixture

(CS15) Tar oil residue heating system in carbon black plant reaches 25 years operation – longer run times, minimum fall-off in performance while processing residue prone to polymerisation and coking CABOT CARBON

Stabiliser inter-reboiler

(CS8) Capacity increased in LNG condensate stabiliser reboiler by improving fluid distribution and reducing film boiling WOODSIDE OFFSHORE PETROLEUM

Heavy wax distillate cooling

(CS6) Wax crystalisation fouling eliminated in heavy wax distillate cooling service with additional benefits of 50% surface area reduction BP OIL